Coordinated effects of air pollution control devices on polychlorinated naphthalenes emissions from coal-fired power...

Coal-fired power plants (CFPPs) are an important industrial source of unintentionally produced polychlorinated naphthalenes (PCNs) emissions. Therefore, field investigations were conducted at six CFPPs and two boilers to analyze emission profiles and removal mechanisms of air pollution control devices (APCDs) of CFPPs. The results showed that electrostatic precipitators (ESP) achieved 41.6% removal efficiency. PCNs were predominantly present in the gas phase (87%), which might be attributed to their semi-volatile nature and strong tendency to volatilize from various matrices. The wet flue gas desulfurization (WFGD) had limited removal efficiency for PCNs, likely because circulating water contains residual PCNs that could be reintroduced into flue gas through gas-liquid exchange. Some CFPPs employed the wet electrostatic precipitator (WESP) after WFGD, which provided additional removal of 41.5%-79.6% but increased higher-chlorinated congeners and toxic equivalent (TEQ) values. Slag, fly ash, and gypsum contained relatively high levels of PCNs (2581-9220 pg/g, 0.05-0.18 pg TEQ/g) and required decontamination treatment. Mono-CN, di-CN, and tri-CN were the dominant congeners in flue gas and solid residues, although their distributions varied across different APCD units. The emission factor of PCNs from flue gas was 29.67 (3.47-61.49) µg/t, with corresponding TEQ values of 2.53 (0.14-7.06) ng TEQ/t, relatively low to other industrial sources. The estimated annual PCN emissions from flue gas and gypsum were 68.2 kg (5.33 g TEQ) and 354 kg (9.16 g TEQ), respectively. Major atmospheric emission provinces (>0.3 g TEQ) included Inner Mongolia, Shandong, Shanxi, Jiangsu, Henan, and Xinjiang, correlating with high coal dependency and industrial concentration.